This project is concerned with elucidation of the critical biochemical roles of copper and zinc in higher animals. Dietary deficiency of copper results in defective crosslinking of the connective tissue proteins, collagen and elastin. Zinc deficiency causes reproductive failure, and pathology of cartilage, bone and skin. The major thrust of the project to date has been the isolation of lysyl oxidase from aortic tissue. This enzyme catalyzes the oxidation of peptidyl lysine to form an allysine residue which is a key intermediate in synthesis of the several known crosslinking compounds. The enzyme has been obtained in a highly purified state and found to contain copper. This element is essential for its activity so that the enzyme may be classed as a copper metalloenzyme. An attempt has been made to isolate a soluble substrate protein for lysyl oxidase. A soluble "proelastin" has been isolated from aortas of copper deficiency chicks. This protein contains a high concentration of lysine and no desmosine or isodesmosine. If it is the true precursor of elastin, as it appears, it should serve as a substrate for lysyl oxidase.